The document “Transverse Mode Selection in Large-Area Oxide-Confined Vertical-Cavity Surface-Emitting Lasers Using a Shallow Surface Relief” (H. Martinsson, J. A. Vukusic, M. Grabherr, M. Michalzik, R. Jager, K. J. Ebeling, A. Larsson; IEEE Photonics Technology Letters, Vol. 11, No. 12, December 1999, pages 1536–1538) describes a method for producing a VCSEL laser, in which a so-called “semiconductor relief” is produced on the surface of the VCSEL laser. The function of the semiconductor relief is to suppress higher modes of the light generated in the active zone of the laser and to leave only the fundamental mode of the light as far as possible uninfluenced. In essence, the functioning of the semiconductor relief is based on the fact that higher modes have a field distribution in the case of which the light is guided principally at the edge of the radiation lobe of the light. In contrast thereto, the fundamental mode has a radiation behavior in the case of which the light is situated principally in the inner region of the radiation lobe of the light. The semiconductor relief thus preferably suppresses higher modes, so that principally or exclusively the fundamental mode of the VCSEL laser is coupled into optical components arranged downstream of the VCSEL laser.
In the case of the VCSEL laser in accordance with the already cited document “Transverse Mode Selection in Large-Area Oxide-Confined Vertical-Cavity Surface-Emitting Lasers Using a Shallow Surface Relief”, the semiconductor relief is arranged on the top side of the VCSEL laser, that is to say above the upper mirror or mirror stack of the VCSEL laser. The semiconductor relief is thus separated from a current aperture of the VCSEL laser by the upper mirror layer of the laser. In the case of the VCSEL laser shown in the document, the current aperture has an area size with a diameter of 15.5 μm. In this case, the area size of the semiconductor relief is understood to be the area size of the inner raised region of the semiconductor relief. The current aperture arranged below the upper mirror layer of the VCSEL laser has an area size (or a diameter) which is larger than the area size (or the diameter) of the semiconductor relief. In concrete terms, the diameter of the current aperture is 20 μm.
The document “Increased-area oxidized single-fundamental mode VCSEL with self-aligned shallow etched surface relief” (H. J. Unold, M. Grabherr, F. Eberhard, F. Mederer, R. Jager, M. Riedl, K. J. Ebeling; Electronics Letters, 5 Aug. 1999, Vol. 35, No. 16) furthermore discloses a method for producing a laser, in which the semiconductor relief and the current aperture are produced in a self-aligning manner. This means that the current aperture is arranged in a concentrically aligned manner relative to the semiconductor relief. The self-alignment is achieved by virtue of the fact that both the position of the semiconductor relief and the position of a mesa structure of the VCSEL laser are defined in the same mask step. The mesa structure is produced in subsequent etching steps, the semiconductor relief inevitably remaining arranged centrally in the mesa structure. The area size of the current aperture is defined in the context of an oxidation step during which the sidewalls of the etched mesa structure are oxidized. This oxidation step effects lateral “oxidation into” the current aperture layer contained in the mesa structure. The semiconductor relief is separated from the current aperture by an upper mirror layer.